MODELLING AND FABRICATION OF CYLINDER HEAD FOR SINGLE

CYLINDER TWO STROKE ENGINE

ABDUL HADI BIN ABD MAJID

A project report submitted in partial fulfillment of the requirements

for the award of the Diploma of Mechanical Engineeringa

t43WJj j.

t1.0

Faculty of Mechanical Engineering

Universiti Malaysia Pahang

NO\TEMBER 2007

ABSTRACT

Automotive technology is very important to people nowadays. To help them to move

someplace to other place in short time. Automotive technology is very fast growing

because of their needed in human life. The two stroke engine is reciprocating engine

in which the piston takes over any valve functions in order to obtain power stroke

each revolution of the crankshaft. This involves the use of ports in the cylinder walls

which are covered and uncovered by movements of piston. Two stroke engines are

used for motorcycles, lawn mowers, chain saw and marine engine. Cylinder Head is

one of the important parts in engine part. The purpose of The Cylinder Head to cover

the movement of piston from Bottom Dead Centre to Top Dead Centre and also

combustion chamber in The Cylinder Head is very important in combustion process.

A

ABSTRAK

Teknologi Automotif begitu penting dalam kehidupan seharian kita. la

menolong manusia bergerak dari satu tempat ke satu tempat yang lain dalam masa

yang singkat. Teknologi Autornotif mudah berkembang kerana kepentingannya

dalam kehidupan manusia. Enjin dua lejang adalah engine perulangan dimana omboh

menganibil alih f'ungsi injap dimana untuk mengekalkan lejang kuasa pada setiap

pusingan crankshaft. mi melibatkan kegunaan ruang dalam silinder dimana ditutup

dan tidak dilindungi oleh pergerakan omboh. Enjin dua lejang digunakan untuk

motosikal, gergaji rantai dan juga enjin kapal. Cylinder Head adalah salah satu

bahagian yang penting dalam bahagian engine. Kegunaan Cylinder Head adalah

melindungi pergerakan omboh dari puncak tertinggi (TDC) kepada puncak bawah

(BDC) dan juga ruang pembakaran dalain cylinder head untuk proses pembakaran

VII

TABLE OF CONTENTS

CHAPTER TITLE PAGE

PROJECT TITLE

SUPERVISOR DECLARATION

DECLARATION

DEDICATION iv

ACKNOWLEDGEMENT V

ABSTRACT

ABSTRAK vii

TABLE OF CONTENTS viii

LIST OF FIGURES xi

LIST OF TABLES xiv

LIST OF APPENDICES xv

INTRODUCTION I

1.1 Introduction 1

1.2 Problem Statement 2

1.3 Objective of Project 2

1.4 Scope of The Project 2

1.5 Project Organization 2

1.6 Author's Contribution 3

VII'

ix

2

LITERATURE REVIEW 4

2.1 Introduction 5

2.2 Internal Combustion Engine 4

2.2.1 Classification of Internal Combustion Chamber 5

2.3 Two-stroke engine 5

2.3.1 Characteristic of Two Stroke Engine 6

2.3.2 The Cylinder Head 7

2.4 Machining Process 8

2.4.1 CNC machining 8.

2.4.2 Rapid prototyping 8

2.5 Problems of Scavenging 13

2.5.1 Type of Scavenging 13

2.5.2 Scavenging Efficiency 14

2.5.3 Perfect Scavenging 14

2.5.4 Perfect Mixing 15

2.5.5 Short Circuiting 15

2.6 Summary 16

3 METHODOLOGY 17

3.1 Introduction 17

3.2 Overall Research Methodology 17

3.3 Engine Overhaul and Measuring 18

3.4 Three Dimensional CAD Drawing 19

3.5 CFD Simulation 20

3.6 CNC Machining 32

3.7 Rapid Prototyping 33

3.7.1 Three Dimensional Printing 33

3.7.2 Spectrum Z510 Specification 34

3.8 Summary 35

x

4 RESULT AND DISCUSSION 36

4.1 Introduction 36

4.2 Solid Work Result 36

4.3 Flow Analysis Result 37

4.3.1 Result For Inlet Mass Flow 0.03 37

4.3.2 Result For Inlet Mass Flow. 0.3 39

4.3.3 Result For Inlet Mass Flow 0.5 40

4.4 Domain Analysis 42

4.5 Fabrication Result 43

4.6 Conclusion 43

5 CONCLUSION AND RECOMMENDATIONS 44

5.1 Introduction 44

5.2 Conclusion 44

5.3 Future Works 45

5.4 Summary 45

REFERENCES 46

APPENDICES

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 The classification of internal

combustion engine 5

2.2 Additive process 11

2.3 The steps for investing casting that

used rapid prototyping wax 12

2.4 Theoretical scavenging process 15

3.1 Flowchart 18

3.2 The original cylinder head 19

3.3 The vernier caliper 19

3.4 Three dimensional drawing of

cylinder head 20

3.5 Three dimensional drawing of

cylinder head 20

3.6 Project wizard 21

3.7 Unit wizard 21

3.8 Fluid type and physical feature wizard 22

3.9 Analysis type wizard 22

3.10 Roughness wizard 23

3.11 Fluid substances wizard 23

xi

xli

3.12 Default wall condition wizard 24

3.13 Initial and ambient conditions wizard 24

3.14 Result resolutions and geometry

resolution wizard 25

3.15 Cosmos flow tree toolbar 26

3.16 Selection of boundary condition 26

3.17 The selection of boundary codition

for flow opening 26

3.18 Selection for second boundary condition 27

3.19 Selection of boundary condition for

pressure opening 27

3.20 Selection of surface goal 28

3.21 Run toolbar 28

3.22 Solver monitor 29

3.23 Three dimensional mesh toolbar 29

3.24 Three dimensional mesh 30

3.25 Cut plot toolbar 31

3.26 Surface plot toolbar 31

3.27 Flow trajectory toolbar 32

3.28 Simulation of cutting process using

masteream software 33

3.29 Spectrum Z510 34

3.30 Three dimensional printing process 35

4.1 Three dimensional computer aided

design (CAD) drawing 36

xlii

4.2 Solver result for inlet mass flow 0.03kg/s 37

4.3 Surface plot result for inlet mass

flow 0.03kg/s 38

4.4 Flow trajectory result for inlet mass

flow 0.3kg/s 38

4.5 Solver result for inlet mass flow0.3kg/s 39

4.6 Surface plot result for inlet mass

flow 0.3kg/s 39

4.7 Flow trajectory result for inlet mass

flow 0.3kg/s 40

4.8 Solver result for inlet mass flow0.5kg/s 40

4.9 Surface plot result for inlet mass

flow 0.5kg/s 41

4.10 Flow trajectory result for inlet mass

flow 0.5kg/s 41

4.11 Domain analysis 42

4.12 Three dimensional printing result 43

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 The characteristic of rapid prototyping

technologies

2.2 Types of scavenging 13

xiv

CHAPTER 1

INTRODUCTION

1.1 Introduction

This project title is modelling and fabrication of cylinder head for single

cylinder two stroke engines. First of all, two stroke engine is a simple and light

engine that piston takes over valve function in operating cycle. It is used for

lightweight power units which can be employed in various attitudes as handheld

power tools [5].It is different from four strokes that had valves to control air flow in

operating cycle. Two-stroke engine was develop since 1876, in 1900 there were

engineers develop this engine with special emphasis on the various solution proposed

for improving gas exchange process [1]. The first two stroke engine for marine was

use in 1905, this engine employed uniflow scavenging with scavenge air valves in

cylinder head and exhaust ports in the lower part of the liner [1]. The characteristic

of two-stroke cycle engine are one power stroke per revolution, scavenging with

fresh charge, direct fuel injection, emissions and addition lubricating. Two-stroke

cycle can be used with both spark-ignition and compression-ignition. Common

applications are where weight low, small bulk, simple construction and high power

output are the prime consideration [1]. For the information, the largest and the

smallest internal combustion engines today are two-stroke cycle engine. There are

some example of special applications, free-piston compressor engines, gas producers

and pulse-jet engine [1]. The cylinder head is made of cast iron or aluminium and it

is strong to distribute the gas forces acting on the head as uniformly as possible

through the engine block [2]. It is also contains spark plug for SI engine or fuel

injector for CI engine.

2

1.2 Problem Statement

Mostly the cylinder head was made by casting process. This project is to

produce the cylinder head by using Rapid Prototyping

1.3 Objective of Project

The main objective of this project is to fabricate a cylinder head for single

cylinder 30.5 cc two stroke spark-ignition (Si) engines.

1.4 Scope of Project

There are four scopes in this project:

i) Reverse engineering.

ii) Three dimension Computer Aided Design (CAD) modelling of original

production cylinder head which is design the original cylinder head using

CAD method that is Solid Work Software.

iii) Simplify the design by just maintaining the key dimension such as clearance

volume, port dimension, and spark plug location in accordance of machining

capabilities.

iv) Fabricating the simplified model cylinder head using Rapid Protolyping

1.4 Project Organization

Chapter 2: Find literature about the basic component of two stroke engines, operating

cycle of two stroke engine and advantage and problem of two stroke engines. This

chapter is about the theory of two stroke engine.

3

Chapter 3: First work in this chapter is drawing the original cylinder head and then

simplifies complex geometry of cylinder head. Then simulate the drawing using

Cosmos Flow Software. After transfer drawing to G-code using Master Cam

Software then machining process is begin. CNC Milling Machine is used for this

process, machine simulator calculate machining time and machine running till

cylinder head is produce.

Chapter 4: The results provide detailed information on results and discussion on this

project which are the prediction of internal flow. Result also from machining process

or rapid prototyping

Chapter 5: Summaries the result and provides conclusions of the present work.

Recommendations for further works are also presented in this chapter.

1.5 Author's Contribution

Three dimensional modelling was developed using Computer Aided Design

(CAD) Software. Introduce the step of in-cylinder flow analysis was predicted by

Cosmos Flow Software. Machining process for cylinder head is using Computer

Numerical Control (CNC) Milling or Rapid Prototyping.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

This chapter concludes about general internal combustion engine, two-stroke

engine characteristic and application then about machining process and also problem

of scavenging.

2.2 Internal Combustion Engine

The purpose of internal combustion engines production of mechanical power

from the chemical energy contained in the fuel. In internal combustion engines, as

distinct from external combustion engines, this energy is released by burning or

oxidizing the fuel inside the engine [2]. The work transfers which provide desire

power output occur directly between fuel air mixture and component of engine. The

internal combustion engines are spark-ignition (SI) and compression-ratio or diesel

engine. Beau de Rochas outlined the conditions under which maximum efficiency in

an internal combustion engine could be achieved, there were the largest possible

cylinder volume with the minimum boundary surface, the greatest possible working

speed, the greatest possible expansion ratio and the greatest possible pressure at the

beginning of expansion [3].

2.2.1 Classification of Internal Combustion Engines

Internal Combustion Engines

Four-SJoke Engine Two-Sfrolce Engine

SI Engine

Petrol Engine Gas Enrine

Carbureted Type Injection Type

I I

BatIery Ignition Magnetd Ignition

CI Engine

Dual FuelllvLiltifuel Divided Chamber Engine Engine

Prechamber Swirl Chamber

Water Air

Reciprocating (Multicylinder) Reciprocating (Single cylinder) Rotary (Wankel)

I I I I 'V' Cylinder In-line Cylinder Opposed Cylinder Single Rotor Twin Rotor

Figure 2.1 : The classification of internal combustion engines [4]

2.3 l'wo-Stroke Engine

Two-stroke cycle lacks separate intake and exhaust strokes, a scavenging

pump is required to drive the fresh charge into cylinder. In one of the simplest and

most frequently used types of two-stroke engine design, the bottom surface of the

piston in conjunction with that portion of crankcase beneath each cylinder is used as the scavenging pump [I].

2.3.1 Characteristics of The Two-Stroke Cycle Engine

i) One power stroke per revolution. Doubling the number per unit time relative

to the four-stroke cycle increase power output per unit displacement volume.

The output of two-stroke engines range from 20% to 60% above those of

equivalent size four-stroke unit. Doubling the number of power strokes per

unit time also halves the intervals between combustion-generated pressure

impulses.

ii) Scavenging with fresh charge. Inherent in the two-stroke cycle is the process

of scavenging the burned gases from the engine cylinder with fresh charge

[1]. Under normal condition, about 20% of fresh charge that enters the

cylinder is lost due to short circuiting to the exhaust. In carburetted spark

ignition engines, the result in very high hydrocarbon emissions and poor fuel

economy compared with four-stroke engine.

iii) Emissions. The emissions characteristics of two-stroke cycle engines are

obviously important and different from four-stroke engine. It is requirements

that must be met depend on the application and are especially strict in

transportation arena. Conventional two-stroke spark ignition engines with

carburettor which are scavenged with a premixed fuel air mixture have

extremely high unburned hydrocarbon emissions due to the significant

amount of short circuiting fresh charge Eli.

iv) Lubrication. Crankcase scavenged two-stroke engine cannot use conventional

four-stroke wet sump lubrication systems because large quantities of oil

would be drawn into combustion chamber.

7

2.3.2 The Cylinder Head

The two-stroke cylinder head either air or water cooled, certainly doesn't

look very exiting but its design has a large bearing on how well engine will run.

Manufactures use various external shapes and cooling fin patterns but the main

requirement is the cooling area is large enough to adequately cool the engine [3].

What are more important are the shape of the combustion chamber and the location

of spark plug location. Over the years, combustion chambers were design but only a

couple are conducive to a reliable, high horse power engine. Researchers have found

that the gases at the very outer limits of the combustion chamber called 'end gases'

that self-ignite to cause detonation. Detonation occurs when a portion of the fuel air

mixture begins to burn spontaneously after normal ignition takes place. End gases are

heated by surrounding metal of the piston crown and combustion chamber and also

by the heat radiating from advancing spark-ignited flame. If the spark flame reaches

the outer edges of the combustion chamber quickly enough, these end gases will not

have time to heat up sufficiently to self-ignited and precipitate detonation. Herein lies

the key to prevent detonation-keep the end gases cool and reduce the time required

for the combustion flame to reach the end gases [3]. The most obvious step that

would satisfy the second requirement is to make the combustion chamber as small as

possible and then place the spark plug in the centre of the chamber. Naturally

combustion flame will reach the end gases in a small combustion space more quickly

than if chamber were twice as wide. Additionally, a central plug reduces flame travel

to minimum [3].

2.4 Fabrication Process Theory

2.4.1 CNC Machining

Computer Numerical Control (CNC) Machine required G-code or M-code to

operating, please refer to appendix to see the list of codes.

8

2.4.2 Rapid Prototyping

Rapid prototyping mostly used in the development stage of new product. It is

a technology which considerably speeds the iterative product development process.

Advantages of Rapid Prototyping:

i) Reduce product development time and cost

ii) Get product to market fast

iii) Enhance communication between marketing, engineering, manufacturing and

purchasing

iv) Present physical model at critical design reviews

V) Perform functional prototype testing before committing to tooling

vi) Generate precise production tooling

Disadvantage of Rapid prototyping:

i) Investment cost very high

ii) Maintenance cost too high

iii) Limitation on materials available

Application of Rapid Prototyping

i) Visualization

ii) Product verification (it is test for functionality)

iii) Iterative product development

iv) Optimization

V) Fabrication or manufacture

vi) Medical and bioengineering

Table 2.1 : The characteristic of rapid protolyping technologies

-

Supply phase

-

Process Layer

creation

technique

Phase change type Materials

Stereolitogra Liquid layer Photopolyinerizatio Photopolymers

phy curing n (acrylates,

epoxies,

Liquid colorable resins,

filled resins)

Solid-based Liquid layer Photopolymerizatio Photopolymers

curing curing & n

milling

Polymers (ABS,

polyacrylate, Fused- Extrusion of Solidification by

etc), wax, metals deposition melted cooling

& ceramics with modeling polymer

binder

Ballistic- Droplet Solidification by Polymers, wax

particle deposition cooling

manufacturi

ng

10

Three- No phase change Ceramic,

dimensional polymer & metal Powder

printingLayer of

powders with powder &

binder binder droplet

deposition

Selective Layer of Laser driven Polymers, metals

laser powder sintering melting powders with

sintering and solidification binder, metals,

ceramics & sand

with binder

Solid Laminated- Deposition of No phase change Paper, polymers

object sheet material

manufacturin

g

Classifications of Rapid Prototyping are:

1) Subtractive (Removal of material)

Additive (Adding of material)

Virtual (Advanced computer base visualization)

Subtractive process

Subtractive process use a computer based prototype technology to speed the

process. If it is for shape verification, a polymer or wax is used but for actual

11

application, a machining process still required. Essential technologies for subtractive

protOtyping are computer, interpretation software, manufacturing software or CNC

machinery [4].

Additive process

This process built workpiece or parts in layer by layer which is slice by slice and

require elaborate software. The steps for this process are:

I) Gain drawing file in CAD file

ii) Computer then constructs slice of a three dimensional parts

iii) Slice analyzed and compiled to provide the rapid prototyping machine

iv) Setup the proper unattended and provide rough part after a few hours

v) Finishing operation sanding and painting

-1 - I

I•J),I

_________ I

Figure 2.2: Additive process

Virtual process

Modelling and simulation of all aspects of prototype by a realistic

visualization. All aspects of design process such as mechanical design, kinematics,

12

dynamics and controls but complicated versions use virtual-reality headgear and

gloves with appropriate sensors. Advantage of this process are instant rendering of

parts where the best design in shortest lead time of complex product and process and

allows the exotic, unconventional design be prototyped, rapidly and cost-effectively.

Applications of Rapid Prototyping

i) Production of individual part. Rapid Prototyping can be used to manufacture

marketable products directly especially involve the polymer parts. Pattern

used in investment casting also produced with Rapid Prototyping technique

shown in figure

flfl

Figure 2.3: The steps for investment casting that used rapid prototlyping wax

ii) Rapid tooling. Typically used to describe a process which either uses as

Rapid Prototyping model as a pattern to create a mold quickly or uses the

Rapid Prototyping process directly to fabricate a tool for a limited volume of

prototypes.

13

2.5 Problems of Scavenging

2.5.1 Type of Scavenging

Scavenging is the operation of clearing the cylinder of burned gases and

filling it with fresh mixture-the combined intake and exhaust process. There are three

classification of scavenging (cross scavenged, loop scavenged, uniflow scavenged).

The problem of scavenging is at there is a short circuiting directly between scavenge

ports and exhaust ports in loop scavenged at 24 crank angles. Uniflow scavenged is

perfect scavenging.

Table 2.2: Types of scavenging

Cross Scavengin^2 I &

Uniflow Scavenging

14

2.5.2 Scavenging Efficiency

The purity of charge can be measure from the success of scavenging in the

cylinder from combustion of preceding cycle. It is controlled by shape of combustion

chamber and scavenging arrangement. Experiment to determine the purity is

relatively simple, consisting only of analysis of gas sample taken during compression

stroke. In German technical literature the term scavenging efficiency has been widely used.

It define as

- Vret - Vret (2.1) llsc— - Vret+Vres

It can be shown that the delivery ratio, scavenging and trapping efficiency are related

by the following equationCrel flSC

Rdel=Iltrap (2.2)

Scavenging efficiency is a term somewhat similar to purity and expresses the

measure of the success in clearing the cylinder of residual gases from the preceding

cycle. Scavenging efficiency indicates to what extent the residual gases means that

all the gases existing in the cylinder at the beginning of scavenging have swept out.

2.5.3 Perfect Scavenging

The fuel air mixture should remain separate from the residual products of

combustion with respect to both mass and heat transfer during scavenging process

[4]. Fresh charges are pumped into the cylinder by the blower through inlet port then

push the products of combustion in cylinder out through exhaust port. However when

sufficient fresh air has entered to fill the entire cylinder volume the flow abruptly

changes from one of products to one of air [4]. This ideal process will represent perfect scavenging without any short circuiting loss.